They Come Back After Being a Slow Pay the Last time?
Tell them you have to collect up front. Remember, have esteem in your business. Your bill collectors do not want to wait to be paid after they provide a service so why should you. You have obviously made a good impression on them if they come back now it##Q##s their turn to show good faith for their mistakes. If they can##Q##t pay up front at least get half or walk.